B-5093

In recent years the public has become more concerned about pesticides and their effects on the environment. From 1987 to 1989, Texas farmers and ranchers treated an average of 15 million acres with insecticides and 20 million acres with herbicides. As stewards of the land and natural resources, farmers and ranchers should strive to use pesticides properly in order to minimize environmental risks.

Pesticides are an integral part of modern farming practices. The proper use of pesticides helps ensure that Americans have an abundant, safe and inexpensive food supply. Pesticides improve crop yields and quality, and help to make farming practices profitable. Sometimes, however, pesticides can threaten wildlife and wildlife habitat.

Small grains such as wheat and sorghum provide food and cover for many wildlife species (Fig. 1). Doves, quail and other birds eat seeds of grain crops after they are planted and after the plants have produced grain. Many birds feed.on insects found in grain fields. Mammals such as rabbits and deer eat the foliage of small grains throughout the winter and spring. Therefore, wildlife may be at risk unless pesticides are used properly.

How Wildlife Are at Risk

Wildlife are directly exposed to pesticides when they eat plants or seeds with chemical residues or when they swallow the pesticide granules themselves. They are exposed indirectly when they eat insects or other animals killed by pesticides. Wildlife that are in fields when pesticides are applied, or that enter fields shortly afterward, may inhale vapors or get insecticides on their skin or in their eyes. Pesticides on an animal's skin or feathers may be swallowed when the animal grooms or preens itself. Pesticides washed by rain into streams, ponds or other wetlands can harm aquatic animals.

Types of Insecticides

Four types of insecticides are used on grain crops:

• organochlorines;
• organophosphates;
• carbamates; and
• synthetic pyrethroids.

Organochlorines, the family of insecticides that contained DDT, dieldrin and aldrin, are rarely used today. Most were banned because of their persistence in the environment and their tendency to biomagnify, or increase in concentration in animals at each higher level of the food chain. Lindane is the only organochlorine insecticide labelled for use in small grains or sorghum in Texas, and it is used only as a seed treatment.

Organophosphate insecticides are widely used. This group includes chlorpyrifos (Lorsban®), dimethoate (Cygon®, Dimate®), disulfaton (Di-Syston®), malathion, parathion and terbufos (Counter®). The toxicity of organophosphates ranges from low (malathion) to high (parathion).

Carbamate insecticides also are commonly used. These include carbaryl (Sevin®), carbofuran (Furadan®) and methomyl (Lannate®). Some carbamate compounds such as carbaryl are not very toxic to terrestrial wildlife (specifically birds), while others such as carbofuran and methomyl are highly toxic.

Synthetic pyrethroid insecticides generally have low toxicity to birds and mammals. However, they are extremely toxic to fish and other aquatic life. With the possible exception of esfenvalerate (Asana XL®) on grain sorghum, synthetic pyrethroids are not often used on small grains or sorghum.

Pesticides can be applied as sprays, granules, dusts, seed treatments or baits. Spray and granular formulations are most common in small grain and sorghum production. Sprays are typically applied after plants are growing, while granular formulations are generally applied at planting time. See Table 1 for a list of insecticides and their toxicities to certain wildlife species.

The hazard of a particular pesticide to any species of wildlife is a product of two factors:

• the chemical's toxicity; and
• an animal's degree of exposure to the chemical.

The toxicity of a pesticide is commonly expressed as either its LD₅₀ (lethal dose) or LC₅₀ (lethal concentration). The LD₅₀ of a particular chemical is the dose that kills 50 percent of the animals exposed to it. The LC₅₀ is the concentration of the chemical in the diet, air or water required to kill 50 percent of the animals exposed. LD₅₀s and LC₅₀s vary among different animal species and are determined by laboratory research. However, for any species, the lower the LD₅₀ or LC₅₀, the more toxic the chemical.

Exposure to a highly toxic insecticide can cause sickness and death. Sublethal doses (doses not large enough to kill an animal) may make an animal sick and alter its behavior. The sickened animal may not return to normal health for several weeks following exposure. Animals made sick by a pesticide are more likely to die if they are exposed again. Sublethal doses also may make animals more vulnerable to predators.

The effects of insecticides on wildlife and fish can be minimized by using the least toxic chemical. An insecticide's hazard to wildlife is based on several factors, including its toxicity to wildlife, the way it is used, and other characteristics such as its persistence in the environment. For example, methomyl (Lannate®) is highly toxic to birds and mammals. However, because methomyl does not persist in the field, careful use of this chemical presents only a moderate hazard to wildlife. In Table 1, insecticides with a rating of "High" may cause wildlife to die or become sick; a "Moderate" rating means an insecticide may cause sickness, but deaths are unlikely: a "Low" rating means the chemical is unlikely to harm terrestrial wildlife when used according to label directions. Hazards may increase for fish or other aquatic animals.

Table 1. Toxicity of common Insecticides and Nematicides Used on Small Grains to Birds, Mammals and Fish

Using Insecticides Safely

Granular Insecticides

Granular formulations of insecticides are often used at planting time. The granules are dropped into the seed furrow and covered with soil. As the plants grow, the roots take in insecticide from the surrounding soil. Granular formulations now labelled for use in small arains or sorahum are aldicarb (Temik®). chlorpyrifos (Lorsban®), phorate (Rampart®, Thimet®) and terbufos (Counter®).

Granular insecticides pose a special threat to birds that feed in fields during planting time. They may swallow the granules accidentally, or mistake them for seeds or grit, and become poisoned. Just a few granules can be enough to kill a bird the size of a sparrow. Whenever granular insecticides are used, the hazard to wildlife can be reduced by completely covering the granules with soil. Be especially careful to disk under granules spilled at row ends where birds are likely to search for food. Be careful not to spill granules while loading them in the hoppers on your planting equipment. If a spill occurs, cover granules with soil. New "closed system" handling technology (Fig. 2) helps to eliminate spills.

Liquid Insecticides

Liquid formulations are usually sprayed on growing plants. The danger to wildlife from liquid insecticides depends mainly on the particular chemical's toxicity. Methyl parathion, disulfoton (Di-Syston®) and dimethoate (Cygon®, Dimethoate®) are highly toxic to wildlife and have been documented to cause wildlife kills. Methomyl (Lannate®) is also highly toxic to wildlife, but has not been reported to cause wildlife deaths when applied according to the label. Carbaryl (Sevin®) and malathion are less toxic to wildlife. Esfenvalerate (Asana XL®) is relatively safe for terrestrial wildlife, but should not be used near ponds or other wetlands.

A major concern when using a spray is that the pesticide may drift from the crop field to other areas nearby, and come in contact with wildlife. It is important to minimize drift by:

• using ground rigs rather than aerial applications when appropriate, especially near sensitive habitats;
• using nozzles and spray pressures designed to produce large droplet size;
• using a drift-control agent;
• not spraying when wind speeds are more than 8 to 10 mph;
• not spraying when the direction of the wind might carry the chemical away from the field to other areas; and
• avoiding ultra-low-volume sprays which produce small droplets.

Fungicides

Fungicides used in small grain and sorghum fields include foliar sprays and seed treatments. Quail and other seed-eating birds may be exposed to fungicides by eating treated seeds shortly after planting. Fungicides currently used on small grains and sorghum have a low toxicity to birds and mammals and do not present a hazard to wildlife. However, some fungicides such as mancozeb (Dithane M-45®, Penncozeb®, Manzate 20®) are toxic to fish. Triadimefon (Bayleton®) and propiconazole (Tilt®) are only moderately to slightly toxic to fish. Fungicide use can be reduced by controlling diseases with cultural practices such as crop rotations, timely planting and variety selection.

Herbicides

About 70 percent of the pesticides used in the U.S. are herbicides. With the exception of paraquat (Gramoxone Extra®, Cyclone®), most herbicides used for small grains or sorghum are only slightly toxic to wildlife (Table 2). The greatest risk to wildlife from herbicides is the effect they may have on wildlife habitat.

Table 2. Toxicity of Herbicides Used on Small Grains and Sorghum.

Many species of wildlife benefit from the seeds or other food produced in and around small grain and sorghum fields. Wildlife rely on the trees, brush, grass and weeds near fields for food and cover. Fencerows, turnrows, borrow ditches, field borders and shelterbelts are important habitats for gamebirds such as quail and pheasants, as well as many species of songbirds and small mammals. Many "weeds" to the farmer (pigweed, sunflowerl are important food sources for birds.

Farmers can provide wildlife habitat near crop areas by planting filter strips. These are strips of land planted to permanent grasses that separate croplands from streams or other wetlands. Filter strips also help to protect water quality by keeping rainfall from washing pesticides and soil into streams. Filter strips should be at least 30 feet wide, and preferably up to 100 feet, to make them useful to wildlife. Cost-sharing programs may be available for developing filter strips. Contact your local Soil Conservation Service office for details.

Integrated Pest Management

Reducing pesticide use is one of the best ways to protect wildlife. However, pesticide reduction must be coupled with good pest management practices so that crop yields and profits do not suffer. Integrated pest management (IPM) is the most effective method of accomplishing this objective. IPM is a system that monitors pest populations and uses all available tactics such as biological, cultural and chemical controls to keep insect pests below economically damaging levels. In an IPM program, pesticides are used only after other tactics have failed to keep pest numbers or damage below the level that causes economic crop loss.

Biological Control

Biological control is the use of natural enemies such as parasites. predators and pathoqens to control Dests. Biolosical control is most effective when used with other compatible pest control practices in an IPM program. These practices include cultural controls such as rotating crops and planting pest-resistant varieties.

Conserving beneficial insects such as ladybeetles, green lacewings, damsel bugs and parasitic wasps is one part of IPM (Fig. 3). It is important to recognize beneficial insects in the field and know how they help control pests. Most insecticides kill beneficial as well as harmful insects, so they should be used only when necessary.

Another kind of biological control involves the use of biological pesticides, sometimes referred to as microbial pesticides. There are nearly 2,000 naturally occurring microorganisms, including bacteria, viruses, fungi or protozoa or their byproducts, that could potentially help control major pests. The most commonly used biological insecticide today is Bacillus thuringiensis or Bt as it is usually called.

For more information on biological controls, refer to Extension publication B-5044, "Biological Control of Insect Pests in Wheat."

Endangered Species

Certain wildlife species are protected by state and/or federal laws under the Endangered Species Act. Texas currently has about 128 species (or subspecies) of animals on its Threatened or Endangered Species list. Also, 28 species lor subspecies) of threatened and endangered plants are found within the state. The misuse of persistent pesticides, especially organochlorines such as DDT, contributed to the decline of birds such as brown pelicans, bald eagles and peregrine falcons. Populations of these endangered birds have increased in recent years since persistent pesticides were removed from the market.

Two other species that are often mentioned on pesticide labels are the Attwater's prairie chicken and the Aplomado falcon, both residents of south Texas. These birds feed in or near croplands where pesticides are often used, and may be harmed by pesticide exposure. Aplomado falcons feed primarily on birds, some of which are migrants that may be exposed to illegal pesticides outside the U.S. The selective use of herbicides has helped prairie chickens by slowing the growth of brush on prime prairie chicken habitat.

There may be pesticide restrictions within your county to protect endangered or threatened species. Contact your county Extension office or the Texas Department of Agriculture for restrictions that may apply in your area.

Interpreting Pesticide Poisoning

Most wildlife poisonings in Texas have involved either organophosphate or carbamate insecticides. Both of these chemical groups affect the nervous system; respiratory paralysis is the immediate cause of death. Animals can be exposed by swallowing or inhaling a chemical, or by getting it on the skin or feathers.

The clinical signs of pesticide poisoning vary with the particular chemical, but usually include respiratory distress, incoordination, tremors, paralysis and convulsions. Usually the animal either dies within a short time or recovers completely. Finding several sick and/or dead animals in an area within a short time is a sign of possible pesticide poisoning.

Birds appear to be the most susceptible terrestrial wildlife to insecticide poisoning. Waterfawl, such as ducks and geese, and passerine birds, such as sparrows, blackbirds, robins and starlings, have been the most common species involved in the poisoning incidents investigated.

According to a U.S. Fish and Wildlife Service report, the insecticides most often implicated in bird poisonings during the 1980s included the organophosphates diazinon, parathion and monocrotophos. In 18 incidents linked to carbamate insecticides, carbafuran was responsible for 16 cases.

Agricultural applications were implicated in about one-third of the die-offs investigated. Parathion has been the most common cause of pesticide related wildilfe deaths in Texas. Most incidents involved geese feeding on wheat fields treated with parathion.

User Ethics

Every pesticide applicator has a legal duty to use the chemical according to label directions. Using pesticides contrary to label directions jeopardizes wildlife and exposes users to criminal prosecution. It may ultimately result in further restrictions on pesticides. Please do your part to see that pesticides are used in a responsible fashion according to label directions.

To Protect Fish and Wildlife Resources

• Use IPM practices in your grain production.
• Choose the pesticide least toxic to fish and wildlife that will control the target pest.
• Protect field borders and other noncrop habitats from pesticide applications.
• Never spray leftover pesticides into wildlife habitats.
• Completely cover pesticide granules with soil, especially spilled granules at the ends of rows.
• Minimize chemical drift by using low-pressure sprays and nozzles that produce large droplets.
• Protect wetlands from spraying and don't spray over ponds or drainage ditches.
• Never wash spray equipment or containers where rinse water could enter ponds or streams.
• Properly dispose of chemical containers.
• Read and follow the instructions on the pesticide label.

Glossary

Biomagnification. The increase in the concentration of a chemical in organisms at each higher level of the food chain.

Direct effects. The adverse effects of coming into contact with a pesticide, specifically when an animal is exposed to a pesticide at a dose high enough to cause toxic effects. Dose. The amount of exposure an organism receives.

Exposure. Contact with a pesticide.

Hazard.The inherent potential for a pesticide to harm fish or wildlife in a particular environment. A product of toxicity times exposure.

Indirect effects. When pesticide use decreases the quantity or quality of wildlife food supply or habitats.

Lethal dose 50 (LD₅₀). The amount of a chemical lexpressed as mg/kg of body weightl that kills 50 percent of a test group; this dose is often referred to as the "acute" toxicity of a pesticide.

Lethal concentration 50 (LC₅₀). The concentration of a chemical in the diet lexPressed as kg/mg of body weight} or in the aquatic environment of a species that kills 50 percent of the individuals over a specified period of time.

Persistence.The length of time a pesticide remains in the environment.

Pesticide formulation. The combination of a pesticide's active ingredient with solvents, carriers, and other inert ingredients that form the pesticide product. Risk. The probability that the application of a pesticide will cause some harm.

Routes of exposure. The pathways by which wildlife are exposed to pesticides: skin contact, oral (through feeding, pruning, feeding and drinking) and inhalation.

Secondary poisoning. When a predator or scavenger becomes poisoned by feeding on contaminated prey.

Sublethal exposure. Exposure to a pesticide at levels that don't kill an animal but that may reduce its chance of survival or harm its ability to reproduce.

Toxicity. The capacity of a substance to harm a specific living organism.

For Additional Information

• "Pesticides and wildlife: a guide to reducing impacts on animals and their habitat." Virginia Department of Game and Inland Fisheries, publication 420-004.

• "Pesticide use and toxicology in relation to wildlife: organophosphorus and carbamate compounds." U.S. Fish and Wildlife Service, resource publication 170.

• "Wildlife and agricultural pesticide use: a review for natural resource managers." North Carolina Cooperative Extension Service, publication AG-475.

• "Managing Insect and Mite Pests of Texas Sorghum," Texas Agricultural Extension Service publication B-1220.

• "Managing Insect and Mite Pests of Texas Small Grains," Texas Agricultural Extension Service publication B-1251.

• "Biological Control of Insect Pests in Wheat," Texas Agricultural Extension Service publication B-5044.

• "Minimizing Wildlife Risks from Agricultural Pesticides." Texas Agricultural Extension Service, video.

This publication is one of a series on reducing risks of pesticides to wildlife. Others in the senes are:

• "Reducing Pesticide Risks to Wildlife in Cotton," B-5094.

• "Reducing Pesticide Risks to Wildlife on Rangeland," B-5096.

• "Reducing Pesdticide Risks to Wildlife," B-5095.

The information given herein is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Cooperative Extension Service is implied.

Educational programs conducted by the Texas Agricultural Extension Service are open to all people without regard to race, color, sex, disability, religion, age or national origin.

Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and June 30, 1914, in cooperation with the United States Department of Agriculture. Zerle L. Carpenter, Director, Texas Agricultural Extension Service, The Texas A&M University System.

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Last modified: June 16, 1997 by Edgar Cross